Effects of warm sea-surface temperature anomalies on the blue petrel at the Kerguelen Islands

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1 Effects of warm sea-surface temperature anomalies on the blue petrel at the Kerguelen Islands Christophe Guinet 1, Olivier Chastel 1, Malik Koudil 2, Jean Pierre Durbec 2 and Pierre Jouventin 1 1 Centres d'etudes Biologiques de Chizë, Centre National de la Recherche Scienti que, F Beauvoir sur Niort, France 2 Centre d'ocëanologie de Marseille, Campus de Luminy, Case 901, F Marseille Cedex 9, France Several long-term studies on Southern Ocean seabirds and seals have suggested a possible link between major declines in breeding performance and El Nin o Southern Oscillation events. We report that the breeding performances and body condition of the blue petrel (Halobaena carulea) on the Kerguelen Islands is depressed by episodic, warm sea-surface temperatures (SSTs) in the winter before breeding. Lagged cross-correlations between SSTs in the Kerguelen sector and the Southern Oscillation Index indicate that warm SSTs were found south of the Kerguelen Islands within a year of, and between 4.2 and 5.4 years after an El Nin o event took place. These results can be discussed with respect to the recently described Antarctic Circumpolar Wave that drives climatic anomalies eastward around the Southern Ocean. Keywords: sea-surface temperatures; Halobaena carulea; blue petrel; breeding success; bio-indicators; Kerguelen Islands 1. INTRODUCTION Studies of the at-sea distribution of seabirds in the Southern Ocean have shown that each water mass can be characterized by distinct assemblages of seabird species (Croxall 1984; Stahl et al. 1985, Pakhomov & McQuaid 1996). Seabird species abundances and assemblages are also in uenced by short- and long-term changes in sea-surface temperatures (SSTs) (Hunt et al. 1981, 1992; Stahl et al. 1985; Veit et al. 1996, 1997). Parallel long-term trends were described across weather, abundance of prey and breeding performance of the kittiwake gull (Rissa tridactyla) over the North Sea (Aebischer et al. 1990). Major seabird breeding failures are associated with warm events occurring in the upwelling systems along the Peruvian coast in relation to El Nin o. Breeding success of Galapagos penguins (Sphenisccus mendiculus) on the Galapagos Islands was seriously depressed by the occurrence of warm SSTs (Boersma 1978), and other studies have related the disastrous e ect of the 1982^1983 El Nin o Southern Oscillation (ENSO) on seabirds (Schreiber & Schreiber 1984; Hays 1986). Several long-term surveys on seabirds and seals breeding on subantarctic and Antarctic localities have shown periodic uctuations in breeding performances possibly in relation to El Nin o events (Croxall 1992; Chastel et al. 1993; Boyd 1993; Guinet et al. 1994). In this study we investigate (i) the e ect of episodic, warm SSTs prior to and during the breeding season on adult body condition and reproductive success of the blue petrel (Halobaena caerulea), an oceanic seabird breeding at the Kerguelen Islands; and (ii) the time-scale relationship between these episodic warm events and the Southern Oscillation Index (SOI). 2. MATERIALS AND METHODS Blue petrels are small, burrow-nesting seabirds (190 g) that forage over oceanic waters and prey mainly on small crustaceans (Ridoux 1994). Data on breeding performances of blue petrels were obtained from a long-term study (1986^1995) on Mayes Island, in the Kerguelen Archipelago, located in the southern Indian Ocean (488 38'S, 'E). A number of measures of the overall breeding performance were made during each breeding season: (i) breeding success was calculated as the number of chicks edged from the number of eggs laid; (ii) hatching success as the number of eggs hatched from eggs laid; and (iii) edging success as the number of chicks edged from eggs hatched. To investigate relationships between SST and adult body condition, blue petrels were weighed during the prebreeding visits (September). During the prebreeding visit, birds stay in their nest and fast for 7^8 d before going back to sea (Chastel et al.1995a). In this study, body condition indices were calculated using individual mass at arrival at the colony from the sea. To make these calculations, empty burrows were checked every 2 d until they were occupied, to record the date of return and the mass of each bird coming from the sea prior to laying (late October). Before laying, adult blue petrels undergo a prelaying exodus (early October to late October; Weimerskirch et al. 1989). For each year, an average body condition index was calculated by scaling body mass to body size (Chastel et al. 1995b). We used SST obtained through satellite remote sensing. Monthly averages of SSTwere calculated from in situ and satellite radiometer measurements obtained on a 18 scale from January 265, 1001^ & 1998 The Royal Society Received 22 December 1997 Accepted 29 January 1998

2 1002 C. Guinet and others E ects of warm sea-surface temperatures on blue petrel 1982 until December Satellite observations were obtained from the Lamont^Doherty Earth Observatory (LDO) at Columbia University and the Integrated Global Ocean Service System (IFOSS), a joint working committee between the Intergovernmental Oceanographic Commission (IOC) and the World Meteorological Organization (WMO). Satellite data were adjusted for biases (Reynolds 1988; Reynolds & Marsico 1993). Spatial scale is of crucial importance in analysing the relationship between environmental factors and seabirds and cetacean distributions (Hunt & Schneider 1987; Jaquet et al. 1996). At the Kerguelen Islands, blue petrels alternate short and long foraging trips during breeding (Chaurand & Weimerskirch 1994a). Antarctic krill (Euphausia superba) has been found in samples coming from long trips (Y. Cherel, unpublished data), suggesting that blue petrels can reach Antarctic waters where SSTs normally range from 71.8 to 1.5 8C (Lomakina 1996). These Antarctic waters are found within a range of 1000 km south of Kerguelen (Reynolds & Marsico 1993), which is consistent with the at-sea distribution of the blue petrel within the Kerguelen sector of the southern Indian Ocean (Woehler et al. 1991). For our analyses, monthly SSTs were obtained on a 18 scale and averaged over a 1000 km semicircle radius surrounding Southern Kerguelen Island (from latitude 'S). Time-series of monthly anomalies in SSTs were determined relative to the monthly mean values for the applicable record length calculated over the study zone, thus removing the average seasonal cycles. A lagged cross-correlation was used to investigate possible relationships between SST anomalies recorded from March preceding the breeding season until the following February (end of the breeding season) in the Kerguelen sector and the breeding performances of blue petrels. However, the occurrence of ENSOs, using the SOI (Rasmusson & Wallace 1983) time-series from 1975 to 1995, also lagged m months from the SSTs observed on the Kerguelen sector. Correlations were run on a data set of SSTanomalies and SOI obtained between January 1982 and December 1995 (n ˆ156), and were calculated for m in a range of 0 to 770 months. Correlations between numerous variables must always be interpreted cautiously, as chance alone may have resulted in a number of signi cant correlations. We used a randomization procedure to evaluate the statistical signi cance of correlation coe cients within our cross-correlation analyses. We calculated a 95% con dence interval on the correlation coe cient using a bootstrap estimation method (Hall1992). Breeding performance parameters were randomly rearranged to SST values times, and the SST anomalies found south of the Kerguelen Islands were randomly rearranged 5000 times for each lag to the SOI. The resulting set of coe cients provides an approximate sampling distribution of the correlation coe cient (Gleason 1988) and, consequently, 95% approximate con dence intervals of the observed value of the correlation coe cient. This procedure allowed us to detect when the correlation coe cient di ered signi cantly from 0 at the 0.05 level (indicating a signi cant shift toward a positive or negative relationship) out of the and 5000 random rearrangements of the data. Results were found to be signi cant when the correlation coe cient was signi cant at the 0.05 level (two-tail test), and when a correlation coe cient value of 0 was not included within the 95% con dence intervals. 3. RESULTS Body condition, breeding success, hatching success and edging success of blue petrels showed signi cant Figure 1. Annual variations (1986^1987 to 1994^1995) in adult condition, breeding success (%), hatching success (%) and edging success of blue petrels on Mayes Island (Kerguelen Archipelago). Sample size for adult condition varied from 18 (1986) to 192 (1991) with an average of 80. Sample size for reproductive performances (breeding success, hatching success and edging success) varied from 21 (1986) to 138 (1993) with an average of 110. Statistics indicate signi cant year-to-year variations. (a) F 8,1036ˆ19.45, p50.001; (b) 2 8 ˆ28.99, p50.001; (c) 2 8 ˆ35.95, p50.001; (d) 2 8 ˆ19.25, p

3 E ects of warm sea-surface temperatures on blue petrel C. Guinet and others 1003 Figure 2. Monthly SST anomaly index for the southern Kerguelen Islands sector from January 1982 to December year-to-year variations ( gure 1). Body condition was low in 1987^1988 and in 1991^1992. Blue petrels also experienced poor breeding performances during these years, with the 1991^1992 season being the poorest when 74% of the eggs laid failed to produce a edgling. Body condition was positively correlated with breeding success and hatching success (Spearman rank correlations, r sˆ0.850, pˆ0.004 and r sˆ0.883, pˆ0.002, respectively, for nˆ9 years). Although the overall breeding success was directly related with hatching success (r sˆ0.850, p for nˆ9 years), no signi cant relationships were found with edging success. Fledging success was not correlated with any other parameters. The SST anomalies observed south of Kerguelen from 1982 to 1995 are shown in gure 2, with warm anomalies occurring during the 1983^1985 and 1991^1993 periods and particularly in In contrast, cold anomalies were detected in 1986 and between 1988 and Annual changes in body condition, breeding success and hatching success ( gure 1) were negatively correlated with year-to-year variation in SSTs observed in each of July, August and September ( gure 3). A negative relationship was found between edging success and SST in both October (egg formation period) and January (chick rearing period, gure 3). No correlations were found between SST anomalies recorded from March to June preceding the breeding season and any of the breeding parameters recorded ( gure 3). The lagged cross-correlation between SST anomalies south of the Kerguelen Islands and the SOI were negatively related for two periods during the study. The rst period corresponded with a lag of 0 to 710 months, indicating that warm waters were found south of Kerguelen within ten months of a warm event taking place in the south subtropical Paci c Ocean. The second period corresponded with a lag of 750 to 765 months, indicating that warm waters were found south of Kerguelen 4.2^5.4 years after the occurrence of an El Nin o event ( gure 4). The window of positive correlation indicated that warm waters were observed at Kerguelen 32^48 months after cold water events (La Nin a) in the south subtropical Paci c Ocean ( gure 4). 4. DISCUSSION This study indicates that warm episodes before the onset of the breeding cycle ( July, August and September) can a ect the body condition and the breeding performances of blue petrels, with hatching success being particularly a ected ( gure 3). The depressed breeding performance of blue petrels in association with warm water events o the Kerguelen Islands can be interpreted in light of their at-sea distribution and foraging ecology. Breeding blue petrels forage mainly over Antarctic waters (Ryan & Cooper 1989) where the distribution of zooplankton communities can be related to SSTs (Deacon 1982; Pakhomov & McQuaid 1996). Our study suggests that when high SSTs occur south of the Kerguelen Islands, either (i) planktonic crustaceans, whose distribution is also related to meso-macro scale SSTs (Deacon 1982; Pakhomov & McQuaid 1996), remained beyond the range of breeding blue petrels, in waters too deep for these surface feeders, or (ii) that prey population levels were low under these environmental conditions. Near Kerguelen, the warmest SST event took place in Interestingly, sampling of physical and biological oceanographic data conducted that year showed (i) that beside the subantarctic and Antarctic zooplankton community typical of the region, fauna typical of tropical latitudes were also present (Ivanchenko et al. 1989; Semelinka 1993), and (ii) that the Polar Front was located 1^2 degrees further south than its multiannual average position (Nagata et al. 1988; Semelinka 1993). Breeding oceanic seabirds are energetically limited during the reproduction by the cost of travelling to and

4 1004 C. Guinet and others E ects of warm sea-surface temperatures on blue petrel Figure 3. Variation in the Spearman correlation coe cient calculated between SST observed from March (previous to the breeding season) until February (at the end of the breeding season) and (a) body condition, (b) overall breeding success, (c) hatching success and (d) edging success of blue petrel over the nine study years. Limits of the 95% con dence interval are indicated by the short, dashed lines. Statistical signi cance of the Spearman correlation coe cient at p ˆ 0.05 is indicated by a long, dashed line on the gure. from distant feeding areas. In poor years, when warm surface waters occurred, the preferred foraging grounds of the blue petrel, in terms of energy acquisition, were probably located too far from their breeding grounds. The blue petrel appears to be a `capital breeder' that needs to accumulate extra reserves to engage in or to persevere a breeding attempt (Chastel et al. 1995a,b). Depletion of the `capital' (i.e. low body condition) very early in the breeding season ( July ^September, more than one month before laying) results mainly in egg desertion (Chastel et al. 1995a). The overall breeding success is directly related to hatching success but not edging success, which indicates that in blue petrels most breeding failure takes place at an early stage of reproduction in relation to the body condition of the birds, whereas the edging success is probably more related to food availability during the chick-rearing period. Nearly half of the total hatching failure occurred during the rst incubation shift (Chastel et al. 1995a). Incubating blue petrels have a threshold mass at which they spontaneously desert their eggs (Chaurand & Weimerskirch 1994b), and birds of a poorer body condition reach this mass more rapidly, and are thus more likely to abandon their eggs (Chastel et al. 1995a). Unlike the July ^September situation, where there is a broadly consistent pattern across breeding performance and body condition of the blue petrels and SST anomalies, the correlations in October and January may be more suspect. However, calculation of the 95% con dence intervals on the Spearman correlation coe cients indicate that the correlations observed in October and January are unlikely to have resulted from chance alone ( gure 3). The negative correlation between SST in January and February and the edging success probably re ects the di culties experienced by adults provisioning chicks. Furthermore, adult body condition during the chick-rearing period plays an important role in regulating allocation decisions and, therefore, parental e ort (Chaurand & Weimerskirch 1994b). However, the relationship found between SST in October and edging success remains unclear. We might also expect the observed SST uctuations to be found on an even broader scale. Blue petrels breeding on the Kerguelen Islands experienced poor breeding performances both in 1987^1988 and in 1991^1992, the latter being the poorest observed. When we compare these observations to the time ^ longitude diagrams of interannual anomalies in SST and sea-ice extent (White & Peterson 1996), these two seasons coincide with largescale positive SSTs and restricted sea-ice extent for the Kerguelen Islands sector (708 E). Our study suggests that the oceanographic conditions of the Kerguelen Islands sector seem to vary in relation to El Nin o activity, and that the breeding performances of seabirds such as the blue petrel are a ected when warm anomalies reach their foraging grounds. The lagged crosscorrelation between SSTs observed in the Kerguelen Islands sector and the SOI showed a negative correlation with periodicity of 4^5 years and with an interfering cold event between the two. This can be interpreted with respect to an eastward propagation of climatic anomalies called the Antarctic Circumpolar Wave (White & Peterson 1996), which takes 8^10 years to encircle the pole. In this system, SST anomalies generated in the south Paci c Ocean follow the hemispheric course of the Antarctic Circum Current, with portions of the anomalies moving north to the southern Peru Current (Humbolt), and the remainder passing through Drake's Passage, spreading towards the equator in the south Atlantic and Indian Oceans. Indeed, poor breeding performances of the blue petrels occurred in years of warm anomalies, associated with the Antarctic Circumpolar Wave reaching Kerguelen (White & Peterson 1996), and our results suggest that these warm SST anomalies should be expected in the southern part of Kerguelen within a year of, and between 4.2 and 5.4 years after, the occurrence of an ENSO event. In relation to global climate warming, we should expect a change of the at-sea distribution of the blue petrel in

5 E ects of warm sea-surface temperatures on blue petrel C. Guinet and others 1005 Figure 4. Lagged cross-correlation, r m, between the SST anomalies for a lag (m) ranging from 0 to 770 months (see text for detailed description) observed south of the Kerguelen Islands from 1982 to 1995 and the Southern Oscillation Index obtained from 1976 to Limits of the 95% con dence interval are indicated by the short, dashed lines. Statistical signi cance of the correlation coe cient at p ˆ0.05 is indicated by a bold, dashed line on the gure. relation to warming waters, as recently described for seabirds foraging over the California Current waters (Veit et al. 1996, 1997). Such a shift in at-sea distribution of the blue petrel is likely to a ect profoundly the breeding performances of that species at Kerguelen. This study is part of the programme 109 `Ecologie des oiseaux et mammiferes marins Antarctiques' (Director: P. Jouventin), and is supported by the `Institut Franc ais pour la Recherche et la Technologie Polaire' and by the programme bio-indicators of the `groupement de Recherche e cosyste mes polaires et anthropisation'. We thank all the eld workers involved in banding and recovery on Mayes Island, D. Besson and D. Capdeville for the data processing, C. Barbraud and X. Bonnet for drawing the gures and A. Hedd and M. Kersten for correcting the English. We thank W. A. Montevecchi and two anonymous reviewers for their useful comments on the rst version of this manuscript. REFERENCES Aebischer, N. J., Coulson, J. C. & Colebrook, J. M Parallel long-term trends across four marine trophic levels and weather. Nature 347, 753^755. Boersma, P. D.1978 Breeding patterns of Galapagos penguins as an indicator of oceanographic conditions. Science 200, 1481^1483. Boyd, I. L Tooth growth in male Antarctic fur seals (Arctocephalus gazella) from South Georgia: an indicator of long term growth history. J. Zool. Lond. 229, 177^190. Chastel, O., Weimerskirch, H. & Jouventin, P High annual variability in reproductive success and survival of an Antarctic seabird, the snow petrel Pagodroma nivea. Oecologia 94, 278^285. Chastel, O., Weimerskirch, H. & Jouventin, P. 1995a In uence of body condition on reproductive decision and reproductive success in the blue petrel. Auk 112, 964^972. Chastel, O., Weimerskirch, H. & Jouventin, P. 1995b Body condition and seabird reproductive performance: a study of three petrel species. Ecology 76, 2240^2246. Chaurand, T. & Weimerskirch, H. 1994a The regular alternation of short and long foraging trips in blue petrel Halobaena caerulea: a previously undescribed strategy of food provisioning in a pelagic seabird. J. Anim. Ecol. 63, 275^282. Chaurand, T. & Weimerskirch, H. 1994b Incubation routine, body mass regulation and egg-neglect in the blue petrel Halobaena caerulea. Ibis 136, 285^290. Croxall, J. P Seabirds. In Antarctic ecology (ed. R. M. Laws), pp. 533^619. London: Academic Press. Croxall, J. P Southern Ocean environmental changes: e ect on seabirds, seal and whale populations. Phil. Trans. R. Soc. Lond. B 338, 319^328. Deacon, G. E. R Physical and biological zonation in the Southern Ocean. J. Deep-Sea Res. 29, 1^15.

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